Preliminary Local Winter 2009/2010 Outlook - Updated

Local Winter 2009/2010 Outlook - Updated October 16 2009

For eastern North Dakota and northwest Minnesota

The Official Winter Outlook from the Climate Prediction Center (CPC), including eastern North Dakota and northwestern Minnesota,for the winter of 2009/2010 calls for the likelihood that temperature will average above the climatological normal, while precipitation will fall within the normal climatic range. The CPC Winter Outlook is available here.

What Is Normal?

The following table shows the 1971 to 2000 Climatic Normals of various winter parameters at several locations in eastern North Dakota and northwest Minnesota.

Note: In the table below, winter is considered the months of December through February

Temperature: (Degrees F)(Dec. - Feb.)

Grand Forks NWS

Fargo

Devils Lake

Warroad

Detroit Lakes

Avg. High Degrees F (Dec. - Feb.)

19.8 / 14.9 / 22.8

20.8 / 15.9 / 22.8

19.8 / 15.5 / 22.8

17.9 / 12.7 / 21.1

20.7 / 17.1 / 24.7

Avg Low Degrees F (Dec. - Feb.)

3.6 / -2.7 / 4.9

4.5 / -2.3 / 5.2

3.5 / -2.8 / 4.9

-0.8 / -9.0 / -1.7

2.2 / -4.8 / 2.5

Mean Degrees F(Dec. Jan. Feb.)

11.7 / 6.1 / 13.8

12.6 / 6.8 / 14.0

11.6 / 6.1 / 13.8

8.6 / 1.9 / 9.7

11.5 / 6.1 / 13.6

# of Days with Highs Below 32F

68 days

68 days

67 days

75 Days

69 Days

# of Days with Lows Below 0F

41 Days

39 Days

40 Days

51 Days

43 Days

Precipitation total: (Dec. - Feb.)

1.99"

1.97"

1.64"

1.80"

2.00"

Total Snowfall (Dec - Feb)

23.3"

22.6"

17.0"

34.3"

26.0"

Total Snowfall (Seasonal)

41.1"

39.0"

35.8"

67.1"

44.5"

Large Scale Climate Forcing Mechanisms

Madden-Julian Oscillation (MJO)

The Madden-Julian Oscillation (MJO) is a relatively short term climatological event on the order of 45 to 60 days in length. An MJO is essentially a wave of relatively warm water that translates from the Indian Ocean, across the tropical Pacific to the west coast of South America. There is typically an upper level wave of energy associated with the MJO that has an effect on tropical weather in the Atlantic basin as well. Recent research indicates that these upper level waves dampen hurricane activity in the Atlantic Basin. For our weather, a strong MJO serves to modulate the strength of a preexisting El Nino or La Nina. At this time there is limited skill at predicting the MJO strength, therefore it does not have a significant impact on the seasonal outlooks. However, shorter term forecasts such as the 8 to 14 day outlook consider MJO influences.

El Nino Southern Oscillation

Fluctuations in sea surface temperatures (SST) across the tropical Pacific Oceanare part of the El Nino/Southern Oscillation (ENSO). The warm phase of the ENSO is called El Nino and the cool phase is called La Nina. During an El Nino, warmer than normal winter weather generally prevails across the northern plains, as the polar jet stream is weakened and displaced north into Canada. This prevents frequent incursions of arctic air into our region. The primary storm track is across the southern states, resulting in generally drier than normal conditions acrossthe northern plains. During La Nina, the storm track is more variable, resulting in intervals of cold and warmth and the potential for significant winter storms. An important aspect of forecasting the winter weather in the northern plains region hinges on the ability to predict the location and magnitude of the largest SST anomalies in the tropical Pacific Ocean. Warm ocean water leads to thunderstorm formation (called convection) and large clusters of thunderstorms that form over the tropical Pacific have a major influence on the pattern of the jet stream. This can influence the location of the storm track and where the areas of warmer and colder weather will prevail across North America.If the most persistent convection in the Pacific is close to the South American coast, this usually results in frequent and persistent cold air outbreaks over the upper plains. If the most persistent convection is closer to the International Date Line, warmer than normal weather usually prevails across our region. Last winter featured near normal sea surface temperatures west of the International Date Line and below normal sea surface temperatures east of the Date Line (La Nina). This, in part, resulted in a snowy and colder than average 2008/2009 winter.

Since July, water temperatures along the Equator have been above normal, indicating weak El Nino conditions. These El Nino conditions are forecast to persist through much of the 2009/2010 winter.

Pacific Decadal Oscillation (PDO)

The Pacific Decadal Oscillation (PDO) is a larger, longer time scale oscillation than ENSO. The PDO affects the ocean temperature anomalies over the central and northern Pacific Ocean, with a time span of decades.Since the PDO affects the Pacific Ocean mainly north of the Equator, and ENSO is primarily a tropical Pacific Oceantemperature anomaly, the PDO can modulate the strength of ENSO.When the PDO is in the positive phase, as it was from 1978 to 1998, El Nino conditions dominate the tropical Pacific Oceanand strong El Nino conditions like the 1982-83 and 1997-98 events are more likely. La Nina events, the negative phase of ENSO, are weaker and less frequent. During the negative phase of the PDO, the opposite is true. The PDO was in the negative phase from around 1947 until 1977.During that time, the Valley Regionsaw generally colder than normal winters. Drier than normal weather is also more prevalent over the northern plains, with greater than 60% of our dry years occurring since 1950 occurring during the negative phase of the PDO. Given the 20 to 30 year cycle of the PDO, we would expect the PDO to trend towards the negative phase over the next decade. The PDO has mostly been in a negative phase since 1998, with occasional warm periods. So what phase will it be in this winter? Based on the current trend, a near neutral phase seems likely. A neutral PDO would have minor overall impacts on the climate. Should the PDO turn back to a cold phase by December, it may try and bias temperatures downward.

NAO

One of the most significant atmospheric variables to affect the winter weather over the northeast third of the United States is the phase of the North Atlantic Oscillation (NAO).The negative phase of the NAO results in cold and snowy weather, as was the case during December of 2000, when Grand Forkshad 19 inches of snow and averaged 11.8F below normal.The following month the NAO went into the positive phase, which typically results in warm and dry weather over our region.January 2001 in Grand Forks was 9.1F above normal with only 3.3 inches of snow!Unfortunately, it is difficult to predict changes in the phase of the NAO, meaning that sharp changes in the winter weather pattern like those of December 2000 to January 2001 can occur without much warning. Recently the NAO has been strongly negative which favors colder than normal weather across the northern plains.

AO

Another strong climate signal is the Arctic Oscillation (AO), a periodic shift in the position of the core of coldest air near the North Pole. When the AO is in its normal [positive] phase, the coldest of air is centered near the North Pole, with pieces occasionally breaking off and moving into the mid latitudes. When the AO is in a negative phase, the cold polar air is shifted much farther south than normal, and a blocking pattern in the atmosphere keeps the colder air shifted abnormally farther south. During the most recent summer of 2009, as well as the record cold summer of 2004, the AO was consistently and strongly negative. This kept the region in a prolonged cold period.

Sun Spot Cycle remains near its minimum

Local research indicates that there is a modest correlation between the minimum of the 11 year Sun Spot Cycle and temperatures patterns in the northern plains. While not as strong a signal as the ENSO, it is more common to see the tendency for colder than normal winters in years when the cycle was near its minimum. The Sun has been in an extended quiet phase since 2006, with only occasional Sunspots developing, and then quickly dissipating. As of mid October 2009, the Sun remains unusually quiet, suggesting the prolonged minimum will persist for the immediate future. More on the current Solar Minimum is available at the NOAA Space Weather Prediction Center.

Long Term Temperature and Precipitation Trends

Between about 1960 and 1997 there was a distinct warming trend in the average winter temperatures over the region. Between about 1998 and 2004 the trend slowed as winter temperatures were not warming as fast. Between about 2004 and 2008 there has been a trend toward slightly cooler winter temperatures (Figure 3). During this same period winter time precipitation has been, overall, showing little significant change (Figure 4). Although weather is certainly not linear, the recent downward trend in temperature and minor increase in winter precipitation are factors in the overall outlook.It is important to note that January 2006, was the warmest January on record for both the Grand Forks Airport and the NWS / University of North Dakota climate weather station. So despite what appears to be a slight downward trend in temperatures, unusually warm winter weather can still occur. It is also important to note that the winter of 2006 was affected by a moderately strong El Nino.

Putting it All Together

Since we are expecting warm ENSO conditions (El Nino), past correlations suggest there’s a 60 percent or greater chance the winter temperature will feature normal to above normal temperatures.Should the PDO enter a negative phase, that would support a tendency toward cooler and drier weather.The NAO appears to be showing a signal that would favor more normal temperatures. The trend of warmer than normal winters during the last 20 years would suggest a warmer than normal winter, although a weak reversal in that trend appears to have started several winters ago. Therefore, the trend signal suggests a tendency towards normal winter weather as well. The NCEP couple ocean/atmosphere model, which successfully predicted the warmer than normal winters of 2000-2001 and 2005-2006, is forecasting above normal temperatures this winter.Taken together, all of this suggests there is a significant signal for the temperature to average above normal across the northern plains this winter.

Below average precipitation is indicated by the warm ENSO conditions, but this is not conclusive. Overall, precipitation tends to show tremendous variability in warm phase ENSO winters, with the El Nino average running about 85% to 95% of climatology. That would suggest snowfall totals this winter of 25 to 35 inches instead of the 'normal' 35 to 45 inches.

Based on local studies, the winter temperature for eastern North Dakota and northwestern Minnesotais expected to favor the warmer side of the normal climatic range. Precipitation should be close to normal. Snowfall should be below normal. One other typical weather pattern observed during warm ENSO winters is an increased frequency of light freezing rain or mist events, due to the more frequent warm spells. Dense fog episodes tend to occur more frequently as well during El Nino winters.

It is also important to note that, even in El Nino winters, deadly blizzards and dangerous wind chills still occur. The major difference is the relative frequency of snowstorms and frigid wind chills is less during an El Nino winter.

Below are images that depict the average weather during winters with ocean/atmospheric conditions similar to what are forecast for this winter. Figure 1 is the 'average' December through February temperature departure from normal, with Figure 2 showing the average precipitation departure from normal for the same period. These are not forecasts, but illustrate what happened during previous El Nino winter seasons. Similar conditions this winter are expected at this time.

Figure 1

Figure 2

Figure 3

Figure 4

An update to this outlook will be issued in late November. For more information contact Mark Ewens, Climate Services Focal Point at 701-772-0720 x327 or email Mark at Mark.Ewens@noaa.gov